I just use IDLE for python as a calculator. You can type in anything at the command line and it'll spit back the answer (or an error). I find it much easier to be able to type 3*4 / (5.**3) and get 0.096000000000000002 back (which I can point a variable to to simplify further steps) rather than have to fiddle around with a calculator GUI. It does have it's quirks though, like the decimal point in the "(5.**" which is there to tell it to use floating point rather than integers (otherwise it returns '0' as the answer), but the quirks are really just an expression of how flexible it is.
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Banned for discussing the recent spate of bannings.